During the last 20 years fish farming has developed into a major industry in the Nordic countries, with Norway as the leading country. The Norwegian sales statistics constituted 63% of a Nordic production of 190.000 tonnes in 1989. Denmark was the second biggest and produced 17%, followed by Finland 11%, and Sweden 4%, Faroe Islands 4%, and Iceland 1%. The gross production, which is the basis for pollution, was estimated at 272 000 tonnes. Atlantic salmon is the dominating species (Norway, Faroe Islands, Iceland), but production of rainbow trout is equally important in Sweden and dominating in Finland and Denmark. A total amount of 3.523 tonnes of phosphorus and 19.262 tonnes of nitrogen was released in the region in 1989. In addition, a variety of chemicals including antibiotics, organophosphates, disinfectants, antifouling agents, chemicals for water treatment and anaesthetics are released from each country. Very few official data are available on the amounts released, except for antibiotics and some other chemicals from Norway. Eutrophication from fish farming is estimated to be a small problem on the west coast of Norway, Iceland, and the Faroe Islands, although local problems may arise in narrow fjords and enclosed areas. Overloading of nutrients is considered to be a major problem in the Baltic, the Belts and parts of Skagerrak and Kattegat. Sedimentation below net-pens affects the bottom fauna, and creates anoxic sediments in all areas with insufficient water exchange. Oxygen deficiency in the bottom water is a potential problem in fjords with a narrow sill. Release of antibiotics and chemicals is considered to be a serious environmental threat to both the wild stocks of fish, and the bottom fauna. Recent studies have shown that oxytetracycline and oxolinic acid are practically undegradable in sediments, and 60-98% of the chemicals are not absorbed by the gut of the fish. The amounts of nutrients released per tonne of fish produced are decreasing due to improved diets, feeding technology, and stricter governmental regulations. The use of antibiotics and some chemicals seems to be a necessity, but can be reduced by increased use of vaccines, improved husbandry practice, reduced fish density, and overall attention to environmental and hygienic conditions. Use of wrasse as a cleaner fish can replace the use of organophosphates to remove sea lice. The introduction of a landbased technology makes it possible to reduce the output of organic material both from smolt- and production farms. New methods of collecting surplus food and dead fish have been developed. Overfeeding can be monitored and controlled by sonic equipment. The environmental problems caused by fish farming are different in the Nordic countries due to geographical, topographical, and physical conditions. The size of production and the governmental regulations vary considerably in the six countries. All forms of intensive aquaculture production are a source of pollution and should be treated as different types of industry.